A proposed project to prevent sewer overflows and basement flooding in Warren could carry a hefty price tag and drive water bills higher.

Engineers hired by the city to develop solutions for boosting the capacity of the waste water treatment system to handle very heavy rain and prevent sanitary sewer overflows have recommended that a major line located on Warren’s east side be connected to the massive Oakland Macomb Interceptor that runs parallel to it in the ITC corridor. The engineers estimated the project, which was the cheapest of four options, could cost $21.75 million.

Each construction scenario studied also would require that installation of new “relief” sewer lines along several of the major east-west roads in the city, at a cost of $6.4 million.

But the head of the Warren Waste Water Treatment Plant and a city engineer said the total price of connecting to the Oakland Macomb Interceptor could total around $30 million.

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“In my opinion, it is the best solution,” said David Monette, who directs operations at the city-owned treatment facility on Warkop Avenue, near 14 Mile Road and Van Dyke.

“We’ve been struggling for years to come up with the best option to deal with this,” he said. “We know we need to do something. We want to do it the best way we can. It’s got to be a long-term solution.”

The Michigan Department of Environmental Quality has forced Warren to make improvements to its waste water treatment system to meet new environmental mandates. During heavy and prolonged downpours, some ground water gets into the city’s sanitary sewer system. When the volume exceeds the capacity of the pipes, partially treated sewage is discharged into the Red Run Drain and raw sewage may back up in basements.

Much of basement flooding has occurred on the city’s east side. After raw sewage backups in 1998, affected residents angrily pleaded with city officials for relief.

A class-action lawsuit involving hundreds of residents was filed in 2000. After a 12-year court battle, the plaintiffs and the city settled the case last October for $1.42 million.

Under the current permit to operate its own waste water treatment facility, the DEQ has mandated that improvements be made to meet national standards to prevent any sanitary sewer overflows, also known as SSO’s, from occurring.

METCO engineers recommended the connection of the Warren waste water system to the Oakland Macomb Interceptor. Two overflow chambers would be constructed below ground, and flow that exceeds the capacity of the city’s 428 miles of sanitary sewers would discharge into a 12-foot-9 diameter section of the Interceptor. The giant sewer stretches 21 miles, from the area of 23 Mile and Dequindre roads, south through Sterling Heights and then to the ITC corridor before sewage reaches a pumping station near Eight Mile and Hoover roads in Detroit.

Any sewage that pours into the Oakland Macomb Interceptor would be measured and eventually flow into the Detroit Water and Sewerage Department system where it would be treated. The city would be billed for that treatment process, which includes disinfectant.

Warren officials on Tuesday took the first formal step toward construction of new sewer lines. The City Council voted late Tuesday to petition the Macomb County Public Works Office to include Warren in the Macomb County Wastewater Disposal District. Joining the district would obligate Warren to pay member fees and charges paid by other municipalities.

The council resolution approved unanimously states, in part: “It is immediately necessary to preserve and protect the public health and welfare of the City of Warren that one of more sewer connections are made to the Oakland Macomb Interceptor to provide emergency capacity for handling excess sewerage flows in Warren’s wastewater collection system during wet weather events.”

City administrators have been negotiating with county Public Works Commissioner Anthony Marrocco to determine who will finance, design, publicly bid and oversee construction of the sewer inter-connections.

After getting a 1-year extension from the DEQ, the city must submit a project design to the state by the end of 2013. Todd Schaedig, facilities engineer at the Warren Waste Water Treatment Plant, said officials expect construction would begin by June 2014.

The project potentially may be financed using low-interest bonds under a state revolving fund for infrastructure projects.

A portion of water/sewer bills collected by the city has been set aside in recent years to fund upgrades that officials expected the state would require. Officials acknowledge that more rate hikes may be in store to pay off bonds over a 20-year period.

According to the METCO report, the other sanitary sewage handling options — each of which would require the relief sewers along the “mile roads” — include:

*Disconnection of footing drains from the sanitary sewer leads at 15,200 homes and redirect the storm water flow to the city’s East Trunk Sewer. The project is estimated at $152.6 million.

*Construction of a 92 million-gallon, 20-foot-deep detention basin plus pumping station improvements, for $74 million; or an underground tunnel approximately five miles long, at $119 million.

In addition to meeting the mandate that no sanitary sewer overflows occur, “these solutions are also required to be designed to alleviate historical problematic basement flooding,” the firm’s report states.

METCO engineers studied the capacity of the Warren’s system based on a so-called “24-hour” rainstorm that MDEQ predicts would occur once every 25 years, producing 3.9 inches of rain.

Records show Warren reported 24 overflows, totaling 443 million gallons of sewage, from the waste water treatment plant in 2011.

Schaedig said Warren records an average of seven or eight overflows of sanitary sewage each year.